1. Field of the Invention
The present invention relates to a vertical milling machine comprising a first milling part and a second milling part.
2. Description of Related Arts
Heretofore, there have been known milling machines of the type that two or more milling rolls or whitening rolls are mounted on one main shaft. For example, U.S. Pat. No. 3,485,280 discloses a horizontal milling machine 81 shown in FIG. 5. In this milling machine 81, starting from the right and going to the left in FIG. 5, a screw roll 83, an abrasive milling or whitening roll 84, an intermediate screw roll 85 and a friction type milling roll 86 are mounted on a horizontal main shaft 82 in order. Around the abrasive milling roll 84 is disposed an annular wire mesh bran discharge member or bran-removing, perforated cylindrical body 87 which cooperates with the abrasive milling roll 84 to form an annular abrasive milling chamber 88, while around the friction type milling roll 86 is disposed an annular wire mesh bran discharge member or bran-removing, perforated cylindrical body 89 which cooperates with the friction type milling roll 86 to form an annular friction milling chamber 90. The abrasive milling chamber 88 is communicated at one end (right end in FIG. 5) thereof with a supply port 91 of the milling machine 81, while the friction milling chamber 90 is communicated at one end (left end in FIG. 5) thereof with a discharge port 92 of the milling machine 81. A feed hopper 93 is provided at the supply port 91, and a resistance board 94 is provided at the discharge port 92. To the resistance board 94 is attached a weight 95 for adjusting pressing force exerted thereby.
According to the conventional milling machine 81 shown in FIG. 5, milling is performed in the following manner.
As grains to be milled are supplied from the feed hopper 93 to the vicinity of the screw roll 83 through the supply port 91, the grains are forwarded generally horizontally by the screw roll 83 and, in the abrasive milling chamber 88, milled under the milling or whitening action by the abrasive milling roll 84 which is being rotated. The grains having been milled in the abrasive milling chamber 88 are forwarded to the friction milling chamber 90 by the intermediate screw roll 85 and, in the friction milling chamber 90, milled still more under the milling action by the friction type milling roll 86 which is being rotated. The grains having been milled in the friction milling chamber 90 are discharged through the discharge port 92 to the outside of the machine against the pressing force of the resistance board 94.
In the conventional milling machine 81 described above, resistance board is provided only at the discharge port 92 of the friction milling part constituting the second milling part, while a discharge part of the abrasive milling part constituting the first milling part is substantially completely communicated with a supply part of the friction milling part constituting the second milling part, and therefore, it is impossible to adjust the degrees of milling or whitening in two milling parts independently.
Further, in the conventional horizontal milling machine 81 described above, since the abrasive milling roll 84 and the friction type milling roll 86 are mounted on one shaft 82, a diameter of the abrasive milling roll 84 is made larger than that of the friction type milling roll 86. This is for the purpose of making peripheral speed of the abrasive milling roll 84 larger than that of the friction type milling roll 86. However, in the above horizontal milling machine, it is structurally difficult to provide uniform contact of the grains with the abrasive milling roll over the whole circumference thereof when the diameter of the abrasive milling roll is increased, and the limit of its diameter is about 30 cm. Accordingly, there is a limit in increase of the size of the machine 81, making it difficult to enhance milling capacity drastically.